The invention relates to an electric motor including a stator and a rotor which includes at least a stack of laminations layered by sheets and provided with slots for receiving rotor windings.
German Pat. No. DE 1 107 804 discloses an electric machine in which the dampening cage of the armature includes poles or pole shoes and is made through dead-mold casting, permanent mold casting or die casting. The short-circuit rings are configured as prolonged pole tips which support the winding, disposed on the pole shank, on the end faces of the pole iron as protection against a deformation or destruction through centrifugal forces, and extend into the space between two neighboring pole windings. Hereby, the high centrifugal forces of the armature are only partly absorbed.
Moreover, it is known, to fabricate the stack of laminations of the armature with end sheets of structural steel or compression rings. The end sheets are configured in the slot area as pressure fingers to effect an axial support. There is no radial force-fitting engagement between end sheet and the short circuit bars in the slot area. The support effect at the bar end must be assumed by the electric sheet. The slots of the electric sheet for receiving the rotor bars are provided with a leakage orifice which is open toward the outer diameter of the sheet. During operation, the rotor bars are pushed by the centrifugal forces to the outside and supported in the area of the leakage orifice at the rod end of the stack of laminations. At this location, the yield point and the strength of the electric sheet restrict a higher operational speed.
It is therefore an object of the invention to provide an electric motor having a rotor configured for high speeds while ensuring a high operational safety.
The posed object is attained by providing at the end face of at least one stack of laminations at least one rotor end sheet which is made of high-strength fine-grain structural steel and exhibits, at least in proximity of the rotor axis, the geometric shape of the sheets layered in the stack of laminations.
These rotor end sheets of high-strength fine-grain structural steel may be made through laser cutting, water-jet cutting or other suitable cutting processes and exhibit a high yield point and strength (770 to 980 Nm/mm2). Thus, material stress during operation at high speeds can be durably coped with. The fatigue strength of these materials ranges for the stated strength zone at 310 to 400 Nm/mm2.
The rotor end sheets are shrunk or pressed onto the finished or unfinished rotor shaft.
In accordance with a further embodiment, the leakage orifices of the rotor end sheets are closed so as to realize a further compaction and thus an increase in the yield point of the electric sheets. Radial forces, applied in particular by the winding head at high speeds can be better absorbed in this manner. In addition, the winding or the winding heads are supported hereby at less stress to the material in the area of the electric sheets. As a consequence of arranging at least some leakage orifices in the rotor end sheet, the electromagnetic properties can be enhanced. By a preferred enlargement of the cross section in the area that is subject to high strain, material stress can be further reduced.
Apart from the rotor end sheets of the individual stacks of laminations, also electric sheets or partial stacks of laminations, positioned axially further inwardly, form a closed leakage orifice and thereby contribute to a further support of the winding and the winding heads, without adversely affecting the electromagnetic properties of the armature.